The game of football is any of several similar team sports, of similar origins which involve, to varying degrees, kicking a ball with the foot in an attempt to score a goal. The most popular of these sports worldwide is association football, more commonly known as just "football" or "soccer". Unqualified, the word football applies to whichever form of football is the most popular in each particular part of the world, including American football, Australian rules football, Canadian football, Gaelic football, Rugby league, Rugby union and other related games. These variations are known as "codes." The Ancient Greeks and Romans are known to have played many ball games, some of which involved the use of the feet. The Roman game harpastum is believed to have been adapted from a Greek team game known as "ἐπίσκυρος" (episkyros) or "φαινίνδα" (phaininda),which is mentioned by a Greek playwright, Antiphanes (388–311 BC) and later referred to by the Christian theologian Clement of Alexandria (c.150-c.215 AD). These games appear to have resembled rugby football.The Roman politician Cicero (106-43 BC) describes the case of a man who was killed whilst having a shave when a ball was kicked into a barber's shop. Roman ball games already knew the air-filled ball, the follis. Documented evidence of an activity resembling football can be found in the Chinese military manual Zhan Guo Ce compiled between the 3rd century and 1st century BC. It describes a practice known as cuju (蹴鞠, literally "kick ball"), which originally involved kicking a leather ball through a small hole in a piece of silk cloth which was fixed on bamboo canes and hung about 9 m above ground. During the Han Dynasty (206 BC–220 AD), cuju games were standardized and rules were established. Variations of this game later spread to Japan and Korea, known as kemari and chuk-guk respectively. By the Chinese Tang Dynasty (618–907), the feather-stuffed ball was replaced by an air-filled ball and cuju games had become professionalized, with many players making a living playing cuju. Also, two different types of goal posts emerged: One was made by setting up posts with a net between them and the other consisted of just one goal post in the middle of the field.